1. Technical Field
The present disclosure relates to improving the launch performance of a vehicle.
2. Background Art
It is known that a vehicle with a smaller displacement engine exhibits greater fuel efficiency than the same vehicle with a larger displacement engine. However, the ability of the vehicle to accelerate is impaired by the smaller displacement inducting less air into the engine to thereby produce power. It is also known that by pressure charging the engine, performance of the smaller displacement engine, at many operating conditions, can be similar to that of the larger displacement engine. More commonly, pressure charging is provided by a turbocharger in which exhaust enthalpy, which would otherwise be exhausted, is recovered as work in an exhaust turbine. The exhaust turbine has a common shaft with a compressor in the intake. The work extracted in the exhaust turbine is used to compress the intake gases to improve power density of the engine. Turbo lag is a known disadvantage of a turbocharged engine. That is, at low engine speed, such as at vehicle launch, little mass is flowing through the engine so that the exhaust turbine spins at a low speed. The engine/turbo system spins up when demanded by the vehicle operator by depressing the accelerator pedal, however with an undesirable delay. If turbo lag could be addressed, fuel efficiency of vehicles could be significantly improved by downsizing and turbocharging without the performance disadvantage at certain low-speed operating conditions. Any improvement in launch performance may also be applied to naturally-aspirated engines.